I have the matrix
x=matrix(c(1,1,2,2,10,10,20,20,21,21,30,30,31,31,40,40,
101,103,102,103,111,112,120,121,120,121,130,131,130,131,140,141),16,2)
I want to repeat each two rows of x a given number of times, that is based on y=c(2,2,2,1,1,1,1,1).
I mean that the first two rows of x are repeated two times (y[1] is equal to 2), the next two rows of x are repeated two times (y[2] is equal to 2), and so on. The last two rows of x are repeated once since (y[8] is equal to 1) is equal to one.
I have tried with rep but it repeates each row, but not each two rows.
I do not want to use any package, just base. Also, I want to avoid any for loop.
>Solution :
x=matrix(c(1,1,2,2,10,10,20,20,21,21,30,30,31,31,40,40,
101,103,102,103,111,112,120,121,120,121,130,131,130,131,140,141),16,2)
s <- rep(seq_len(8), c(2,2,2,1,1,1,1,1))
x[as.vector(rbind(s*2 -1, s*2)),]
##>
##> [,1] [,2]
##> [1,] 1 101
##> [2,] 1 103
##> [3,] 1 101
##> [4,] 1 103
##> [5,] 2 102
##> [6,] 2 103
##> [7,] 2 102
##> [8,] 2 103
##> [9,] 10 111
##>[10,] 10 112
##>[11,] 10 111
##>[12,] 10 112
##>[13,] 20 120
##>[14,] 20 121
##>[15,] 21 120
##>[16,] 21 121
##>[17,] 30 130
##>[18,] 30 131
##>[19,] 31 130
##>[20,] 31 131
##>[21,] 40 140
##>[22,] 40 141